The present invention relates generally to a continuous method and installation for bleaching a textile fabric web, and more particularly to a continuous method and installation for bleaching a textile fabric web having improved hydrophilic properties.
In a bleaching process, a bleaching liquor, which contains for example, a sodium hydroxide solution and peroxide, is applied, after a prewashing step, to a textile fabric web made entirely or mostly of cotton. The bleaching liquor acts on the fabric web in a steaming machine for a specified dwell time. The applied chemicals and the dissolved substances are subsequently removed from the fabric web by an intensive washing process. The web is then ready for the dyeing process.
This known, standard-type process produces a fabric web having a good degree of whiteness and freedom from shells or husks, but it results in hydrophilic properties that often leaves much to be desired. This means that the fabric web does not absorb the dye liquor vigorously enough. The hydrophilic property is determined by how much of the wax and grease found on the cotton fiber can be dissolved by the NaOH treatment. If the quantity dissolved is not quite complete so that some of the wax and grease remain on the fabric web, the hydrophilic property of the web is inferior and, accordingly, the liquid dye is poorly absorbed.
After the fabric web traverses the steaming machine, the applied chemicals are not yet completely spent. Rather, a certain portion of residual chemicals remains on the fabric web when it enters the washing unit.
The washing unit is formed from several individual washing machines, which are arranged one behind the other and which may be designed as roller vats, for example. In known installations, this type of series of washing machines is operated according to the counter-flow principle for economic reasons. The term "counter-flow" means that the fresh water is added at the end of the row and flows in a direction opposite to the direction in which the fabric web is fed from one washing machine to the other. The fresh water is then conducted into the drain duct of the washing machine that is last relative to the direction of flow and first relative to the direction in which the fabric web is fed (DD-A-63 454; DE-C-3 119 869). Accordingly, with respect to the bleaching installation, the fabric web was confronted with a large supply of permeated liquid after traversing the steaming machine, which was at once drained off in the first washing machine. As a result, the residual chemicals on the fabric web were rinsed off and removed right at the beginning of the process.
The present invention is directed to the problem of improving the treatment of a fabric web in a bleaching installation to improve the hydrophilic properties of the fabric web.